The application of coatings to surfaces has been achieved in a variety of ways, such as by spin coating, dip coating, spray coating, and flow coating techniques. While these techniques have been successful when used to coat smooth surfaces, such as the optical surface of single vision ophthalmic lenses, they have not been entirely satisfactory. For example, such techniques have often resulted in a build-up of a coating material at the outer edge of the lens that causes optical aberrations.
Such techniques have proven to be even less satisfactory when used to coat irregular surfaces, such as those present on multi-vision ophthalmic lenses, particularly those made from plastic. Such lenses generally have segments that project abruptly away from at least one major optical surface of the lens. Coating solutions applied to these optical surfaces by spin, dip, spray, or flow techniques must flow around and over these segments, with the resulting coating generally exhibiting flow marks around the projection and being thick at the intersections of the segment and the optical surface.
A further disadvantage of conventional techniques of applying coatings to optical elements is that they often have high labour and capital requirements. Furthermore, any yield loss at the point of coating results in total loss of a high valued product at the end of its manufacturing cycle.
In response to these difficulties, an ‘in-mould’ coating technique was developed for manufacturing ophthalmic lenses. The method comprised applying a single coating to a face of a mould, partially curing the coating upon the mould, subsequently assembling the moulds, filling the moulds with a lens monomer, and curing the lens monomer to form a hard lens.
However, a limitation of this in-mould technique is that it does not allow for the provision of a coating that is both highly abrasion resistant and has excellent cross hatch adhesion to the lens substrate. Furthermore, it has not proven to be possible to incorporate other desirable optical properties to the coating produced by this technique.
It is an aim of the present invention to provide an improved in-mould coating technique that is capable of being used to produce coated optical elements such as ophthalmic lenses.